1. Field of the Invention
The present invention relates to a dynamic absorber for a pendulum type structure such as a cable suspension transporter (gondola lift).
2. Description of the Prior Art
In recent years, cable suspension transporters used in skiing grounds or sightseeing places have been under discussion for adoption as transport means in cities, by virtue of their low construction cost as compared with monorail and the like. However, the largest disadvantage of those cable suspension transporters is their weakness to wind. Because of their structure, transporters suspended from steel cables are easily affected by the drag of wind. Accordingly, presently the operation of such transporters is stopped at a wind velocity of approximately 15 m/s, but they need to be operable for at least a wind velocity around 20 m/s to useful as a means of city transport. Thus, a technique for damping wind-excited vibration of cable suspension transporters gains considerable public attentions. However, general translational motion models cannot be applied to this technique, which necessitates a new technique for damping the vibrations of rigid pendulums.
As a concrete damping techniques for cable suspension transporters, there has conventionally been proposed using gyroscopic moment (Nishihara, Matsuhisa, and Sato, Vibration Control Mechanism Using Gyroscopic Moment, Transactions of JSME, C, 57-534(1991), 497; Matsuoka and Nishida, Preventive Control of Swing of Gondola Lift by Using Gyroscopic Moment, Proceedings of JSME, No. 920-55, B (1992), 178). As for these, a trial product for six-passenger transporter has already been manufactured (Kanki H., Nekomoto Y. and Monobe H., Development of CMG Active Vibration Control Device for Gondola, The First International Conference on Motion and Vibration Control (MOVIC), (1992), 310), in which swing caused by wind is reduced to about 1/3. However, this has a problem in that since the cable suspension transporter is not connected to an external power supply, there arises a need of developing a power-saving system which can be driven by batteries.
Further, there has been proposed another damping technique using dynamic absorber on which there has been discussed using a spring-mass type absorber or pendulum type absorber (Sato and Chishima, On Reduction in Swing of Cable Suspension Transporter by Pendulum-Type Dynamic Absorber, Proceedings of JSME, C, No. 910-17(1991), 528). The spring-mass type absorber, when provided in proximity to the center of gravity of the transporter, would operate in such a way that the mass of the transporter and that of the dynamic absorber will move integrally with each other, resulting in no damping effect.
On the other hand, as for the pendulum type absorber, in the case that it is provided below the transporter as a double-pendulum system, since it requires a long arm of an additional pendulum for optimal tuning, it becomes impractical. Moreover, it is also discussed that the length of the arm be shortened by reducing the natural frequency as a result of inclining the pendulum (Sato, Hosokawa, and Chishima, Control of Swing of Cable Suspension Transporters by Inclined Pendulum Type Damper, Proceedings of JSME, A, No. 920-55(1992), 592). In this case, there would arise a problem as to the position where the dynamic absorber should be provided.